Hose assemblies for conveying fuel and other volatile corrosive materials, such as liquified halogen gases are well known in the art. Such assemblies are exposed to a variety of fuel mixtures, fuel additives, and caustic or corrosive materials in addition to being exposed to extreme temperatures and pressures. Thus, such hose assemblies must be resistant to chemical, environmental, and physical degradation as a result of chemical exposure, environmental exposure to heat, and physical degradation resulting from bending and repeated movement or forces applied to the assembly.
Polymeric fluorocarbon materials such as polytetrafluorethylene possess the requisite chemical and temperature resistant properties for most fuel hose applications. Unfortunately, however, polymeric fluorocarbon materials exhibit relatively more poor tensile and hoop strengths. As a consequence, such fluorinated materials are prone to kinking. Such kinking remains permanent and provides a continual resistance to fluid flow through the hose assembly. Moreover, as a result of a fluorinated material's low tensile strength, attachment of securing or coupling members to the hose assembly is substantially compromised.
Various approaches have been described for offering additional strength to a polymeric fluorocarbon liner. One approach involves braiding fibers about the inner fluorocarbon liner. The braided fibers offer additional strength to the fluorocarbon liner resulting in a hose assembly that resists kinking. In the example of such an approach is disclosed in U.S. Pat. No. 5,124,878, filed Jul. 12, 1991, and assigned to the assignee of the subject invention. The hose assembly described in the '878 patent includes an inner fluorocarbon polymeric liner, a braided reinforcing layer disposed about the exterior of the inner liner, and is characterized by including an organic polymeric material dispersed in the reinforcing layer which connects the reinforcing layer to the inner liner thereby providing a hose assembly which is stronger and more kink resistant.
An additional example for strengthening an inner fluorocarbon liner with an outer liner while also increasing flexibility is shown in U.S. Pat. No. 3,023,787 to Phillips et al. The Phillips et al. patent discloses a convoluted hose assembly having a fluorocarbon inner liner constructed of many layers of helically wrapped Teflon.RTM. tape. Convoluted hoses are typically employed because they provide flexibility to a fluorocarbon hose assembly, however, convoluted hose assemblies have inherent weaknesses. A reinforcing strip consisting of reinforcing fibers coated with a plastic material is wrapped about the inner layer to provide additional strength to the assembly due to the inherent weakness of wrapped convoluted core construction. In its final assembly, a metal braid is applied to the outside of the hose assembly to impart greater strength. Hose assemblies of the type described in the Phillips et al. patent have several inherent drawbacks. First, because the inner liner is formed by helically wrapping layers of a fluorocarbon tape, it requires a greater amount of fluorocarbon material to be utilized in order to construct the inner liner which adds to both the cost of constructing the hose assembly and to the labor intensity of constructing the hose assembly. The most prominent drawback associated with hoses of the type disclosed in the Phillips et al. patent includes failure of seams created by helically wrapping layers of Teflon.RTM. tape. These failures occur due to inherent weaknesses in bonding the seams created by the overlapping layers of tape which, under internal pressures and prolonged movement are prone to leakage. Furthermore, due to the continuous seam which is created during core wrapping, wrapped or convoluted core hoses are highly prone to effusion of molecules from the interior of the hose to the exterior environment. This inherent location for molecular effusion of the contents of the wrapped core hose assembly allows for the rapid escape or release of potentially toxic, caustic, and environmentally harmful materials from the hose assembly. Effusion is defined as the movement of gas molecules through small holes. Again, due to the nature of convoluted or wrapped hose construction, materials are more likely to effuse from a prior art hose assembly even when the hose assembly is intact and not damaged or worn due to extended use. In addition, the seams create undulations within the inner liner which cause disruption in the flow of liquids therein which could give rise to increased electrical charge buildup within the hose.
Additionally, prior art hose assemblies utilized for conducting corrosive or hazardous substances are inherently prone to chemical degradation due to spillage of the corrosive or hazardous material on the exterior of the hose assembly or from the build-up or pooling of effused corrosive or hazardous material on the exterior of the hose assembly. The problem of spillage or pooling of effuent on the exterior of the hose assembly can cause localized degradation of the hose assembly due to acid formation in the case of halogen spillage or effuent. The localized degradation can cause premature failure of the hose assembly. Additionally, the proneness of prior art hose assemblies to chemical degradation from spillage or effuent pooling is especially problematic in hose assemblies which utilize a metallic or non-chemical resistant outer layers or jackets in order to provide strength and flexibility to the hose assembly. Metallic or non-chemical resistant outer layers or jackets are especially prone to degradation from acid formation or corrosive materials which may be spilled or effuse from the interior of the hose assembly and pool on the exterior of the hose assembly.
Therefore, it would be desirable to have a hose assembly which includes an extruded polymeric fluorocarbon inner liner which is resistant to effusion of molecules from within the hose assembly while additionally possessing an outer layer which is resistant chemical degradation while also increasing flexibility and reducing kinking of the inner liner.